The development of novel catalytic systems exhibiting unique reactivity and high enantioselectivity requires the synthesis of chiral ligands for transition metals. Generally, some of the most successful chiral ligands have been chelating phosphines possessing a C.sub.2 symmetry axis.
Many of the chiral phosphines known in the art have at least two aryl substituents on the phosphorous, rendering that center relatively electron poor. The mechanism of asymmetric induction using these phosphines has been linked to the proper conformational relationship between the phenyl groups on the phosphorous centers.
More recently, chiral phosphines having relatively electron rich phosphorus centers have been reported. Brunner et al., Journal of Organometallic Chemistry, Vol. 328, pp 71-80 (1987) teach 3,4-disubstituted phospholanes derived from tartaric acid having chloro, methoxy, or dimethylamino substituents. These were complexed with manganese and rhodium and used as catalysts in the hydrogenation of alpha-N-acetamidocinnamic acid. Relatively low optical yields of (S)-N-acetylphenylalanine of from 6.6% enantiomeric excess to 16.8% enantiomeric excess were obtained.
S. R. Wilson and A. Pasternak, Synlett, pp. 199-200, April 1990 describe the preparation of (2R,5R)-1-phenyl-2,5-dimethylphospholane and its use in an enantioselective Staudinger reaction (reduction of azides with phosphines). Here the chiral (2R,5R)-1-phenyl-2,5-dimethylphospholane is used as a stoichiometric reactant, not as a catalyst.
M. J. Burk et al, Organometallics, Vol 9, pp. 2653-2655 (1990) describe a series of mono and bidentate 2,5-disubstituted phospholanes and demonstrate their use as ligands in asymmetric catalysis. Rhodium complexes bearing the disclosed phosphine ligands were prepared and tested as catalyst precursors for the enantioselective hydrogenation of unsaturated substrates. The phosphorous atoms in the disclosed bis phospholanes are linked by two- or three-carbon methylene bridges.
M. J. Burk et al, Angewandte Chemie, International Edition in English, Vol 29, pp 1462-1464 (1990) disclose tris phospholane tridentate ligands with C.sub.3 symmetry.
U.S. Pat. No. 5,008,457 issued Apr. 16, 1991, discloses mono, bidentate, and tridentate phospholanes useful as transition metal ligands in asymmetric catalysis and processes for their preparation as in the above two Burk et al. references.
Several references teach various synthetic routes for the preparation of cyclic sulfites or cyclic sulfates. However, these contain no disclosure nor suggestions that the disclosed reaction sequence could be used to prepare symmetrical chiral 1,4-diol derived cyclic sulfites or 1,4-diol derived cyclic sulfates.
Y. Gao and K. B. Sharpless, J. Am. Chem. Soc., 110, 7538(1988) disclosed the reaction of 1,2-diols, including some chiral 1,2-diols, with thionyl chloride to form 5-membered ring cyclic sulfites which, upon oxidation with NaIO.sub.4 and catalytic RuCl.sub.3, are converted to 5-membered ring cyclic sulfates.
B. M. Kim and K. B. Sharpless, Tetrahedron Lett., 30, 655(1989) report further on the preparation and reactivity of 5-membered ring cyclic sulfates derived from 1,2-diols.
U.S. Pat. No. 4,924,007 discloses a process for the preparation of 5- and 6-membered ring cyclic sulfates from 1,2- and 1,3-diols by reaction with concentrated sulfuric acid at 150.degree. C. to 250.degree. C.
U.S. Pat. No. 4,960,904 discloses a process for the preparation of 5- and 6-membered ring cyclic sulfates from 5- and 6-membered ring cyclic sulfites by oxidation.
Great Britain Patent 944,406 discloses a process for the preparation of 5- and 6-membered ring cyclic sulfates from 1,2- and 1,3-diols by reaction with first, thionyl chloride to form 5- and 6-membered ring cyclic sulfites and second, an oxidizing agent.
J. Lichtenberger and J. Hincky, Bull. Chim. Soc. Fr, 1495(1961) describe the synthesis of a cyclic sulfate from 1,4-butanediol.
E. J. Lloyd and Q. N. Porter, Aust. J. Chem., 30, 569(1977) describe the syntheses of cyclic sulfates from 1,4 -butanediol and 2,5-hexanediol.
N. Machinaga and C. Kibayashi, Tetrahedron Letters, Vol. 31, p. 3637 (1990), describe the synthesis of an unsymmetrical, chiral 1,4-diol derived cyclic sulfate and the synthesis of an unsymmetrical, chiral 2,5-disubstituted pyrrolidine from it.
A continuing need exists for transition metal complexes providing high levels of stereochemical control and asymmetric induction in stoichiometric and catalytic transformations. A need also exists for chiral ligands having a high degree of enantiomeric purity for use in the preparation of transition metal catalysts, and for efficient synthetic routes for the preparation of such chiral ligands.
It therefore an object of the present invention to provide cyclic sulfate compounds for use in preparation of chiral bis (phospholane) ligands.
It is a further object of the present invention to provide bis (primary phosphine) compounds for use in preparation of chiral bis (phospholane) ligands.
It is a further object of the present invention to provide a novel bis (phosphonite) compound for use in preparation of a specific bis (primary phosphine).
It is a further object of the present invention to provide either enantiomer of chiral phospholane ligands having a high degree of enantiomeric purity for use in the preparation of transition metal catalysts.
It is a further object of the present invention to provide a process for the preparation of either enantiomer of chiral phospholane ligands.
It is a further object of the present invention to provide transition metal complexes which afford high levels of stereochemical control and asymmetric induction in stoichiometric and catalytic transformations.
It is a further object of the present invention to provide a hydrogenation process using the transition metal catalysts of the present invention.